Composite glass article and method of manufacture

ABSTRACT

A composite glass article having a chemically modified ceramic surface whose coefficient of thermal expansion is lower than that of the glass substrate is produced by exposing the glass article maintained at a temperature above its annealing point (typically 500° C.) and below its softening point (soda-lime about 725° C.; borosilicate about 800° C.) to an atmosphere containing prescribed metalorganic compounds. The chemically modified ceramic surface in maintained in compression and is a ceramic consisting of members from a specific group of oxides dependent upon the type of glass comprising the substrate. The method for forming the glass composite article includes applying the metalorganic mixture while the glass substrate is maintained at a temperature above its annealing point (typically 500° C.) and below its softening point (soda-lime about 725° C.; borosilicate about 800° C.) to an atmosphere containing prescribed metalorganic compounds. A chemical reaction occurs producing a chemically modified ceramic coating which is in compression relative to the substrate thus conferring increased strength to the glass article.

“This application is a divisional of application(s) application number08/582,710 filed on Jan. 4, 1996 now abandoned” InternationalApplication 08/799,292 filed on Feb. 13, 1997 U.S. Pat. No. 5,910,371and which designated the U.S.

BACKGROUND OF THE INVENTION

Efforts have long been made to strengthen glass articles, including flatglass, glass containers formed of ordinary soda lime glass, andborosilicate low expansion articles. These efforts have been directedprimarily towards tempering of the glass by a variety of processesincluding chemical tempering and air tempering which involves rapidcooling of the surfaces of a heated article to place the surfaces incompression. Additionally, it has long been known to apply coatings toglass articles, tempered as well as non-tempered, for a variety ofpurposes. These processes are exemplified in the following prior artpatents: U.S. Pat. Nos. 5,108,479; 5,089,039; 5,085,805; 5,043,002;4,728,353; 4,615,916; 4,530,857; 4,457,957; 3,996,035: and 3,850,679.

DISCLOSURE OF THE INVENTION

Under the present invention, the glass article is treated while in aheated condition at or above its annealing temperature (typically 500°C. for soda lime and borosilicate glasses) and below the softening pointtemperature (typically 725° C. for soda lime and 800° C. forborosilicate glasses) with chemicals selected from certain groups ofchemicals depending upon the formulation of the glass substrate. Thus,the groups of chemicals used and the way in which they are combined,will vary depending on whether the substrate is (1) ordinarysilica-soda-lime glass such as that used for windows or glass containersor (2) low expansion borosilicate glass such as that used for scientificlaboratory glassware. The present invention may be used forstrengthening a wide variety of glass articles including, but notlimited to, flat glass, bent glass, glass containers, glass drinkingtumblers, scientific glass, and solar collectors.

Under the present invention, the glass, while in a heated condition at atemperature above its annealing point (typically 500° C.) and below itssoftening point (typically 725° C. for soda lime and 800° C. forborosilicate glasses) is exposed to an atmosphere containingmetalorganic compounds from a specific group. The atmosphere may begaseous or may include liquids in a fine mist obtained by spraying. Theheat from the glass maintained in the above mentioned proper temperaturerange causes the metalorganic compounds to decompose leaving achemically modified ceramic surface. The group of metalorganics for usewith a specific type of glass will vary depending on the coefficient ofthermal expansion of the glass and is selected such that the chemicallymodified ceramic surface has a coefficient of thermal expansion lowerthan that of the unmodified glass substrate. In contrast to prior artcoatings in which there is a sharp demarcation between the metallicoxide coating and the glass, under the present invention, there isformed a chemically modified ceramic surface created by chemicalreaction of the decomposing metalorganics with the surface of theunmodified substrate. If desired, the glass article, concurrent with theapplication or immediately after the application of the metalorganiccompounds, may be subjected to an infrared radiation treatment toenhance the chemical reaction. As a result of the fact that thechemically modified ceramic surface has a lower coefficient of thermalexpansion than the substrate, the chemically modified ceramic surfacewill, upon cooling of the composite glass article (i.e., the glasssubstrate with the chemically modified ceramic surface), be placed incompression thus providing greater strength for such composite glassarticle as compared to a similar article formed solely from a similartype of glass without the benefit of the prescribed treatment with themetalorganic compounds.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a prior art glass article with a coatingas heretofore known.

FIG. 2 is a sectional view of the composite glass article of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Broadly, the present invention is for a composite article and method offorming in which the article includes: (1) the article of glass known asthe substrate having a predetermined coefficient of thermal expansion,and (2) a chemically modified ceramic surface having a coefficient ofthermal expansion lower than the coefficient of thermal expansion of thesubstrate.

Referring now to FIG. 1, there is shown in section a fragmentary portionof a glass article generally designated by the numeral 10. This articleconsists of a layer of glass 12 and a coating layer 14 applied theretoby one of the processes disclosed in the prior art references givenabove or by other means known in the art. For example, U.S. Pat. No.4,530,857 discloses a process for manufacturing a glass article with afunctional coating containing a metal oxide as the principle component.In this process a glass container heated to at least 800° F. is sprayedwith a glass coating formulation comprising monoalkyltin trihalide andabout 0.5 to 10 parts by weight per hundred parts of monoalkyltintrihalide as a solubilizing material. As another example, U.S. Pat. No.5,108,479 discloses a process for manufacturing glass with a functionalcoating wherein a film which contains a metal oxide material such as aalkoxide of Ti, Ta, Zr, In, Sn, Si, or the like is applied to apredetermined portion of a glass plate and then subjecting the glassplate to a bending treatment and/or tempering treatment by heating thesame with simultaneous baking of the printed film to thereby form thefunctional coating containing the metal oxide as the principleconstituent. Thus, if the prior art example of FIG. 1 represented theteachings of U.S. Pat. No. 5,108,479, the coating 14 is a metal oxidehaving been converted from a metal alkoxide applied to the glass plate12. The thickness of such coating according to the prior art teachingsof U.S. Pat. No. 5,108,479 is on the order of 400-2300 Angstroms. Itwill be noted that under the teachings of U.S. Pat. No. 5,108,479 andother prior art known to the applicants, there is a sharp line ofdemarcation 16 between glass layer 12 and the coating layer 14.

The metal oxide coating process taught in the prior art, especially inU.S. Pat. No. 4,530,857, provides a metal oxide coating layer 14 towhich a polymer coating will adhere thus conferring lubricity andresultant scratch resistance to the article. The strength of the articleis not increased by this treatment.

The chemically modified ceramic surface taught by this invention placesthe substrate in a state of compression that strengthens the article.This modified surface also enhances the chemical durability. FIG. 2 is adiagrammatic representation of a glass composite article 20 of thepresent invention. The glass composite article 20 includes the soda-limesubstrate glass 22 and the modified ceramic surface 24 denoted by atriangle extending into substrate 22.

The metallic, ceramic coating of this invention are prepared from acoating composition including a metal alkoxide and a silicon alkoxide.The alkoxides are represented by the formulas R_(n)XO_(n) and R₄SiO₄wherein X is Al, Ti, Ta, Zr, In or Sn; each R group is an alkyl radicalhaving 1 to 8 carbon atoms; and n is an integer ranging from 1 to 4.Preferably, R is an alkyl radical having 1 to 3 carbon atoms, X is Al,and n is the integer 3.

Pyrolysis of the organo-metallic compound leaves a uniform ceramiccoating on the substrate which is a mixture of a metal oxide and silicondioxide. For example, pyrolysis of a mixture of aluminum ethoxide((C₂H₅)₃ ALO₃) and tetraethyl silicate ((C₂H₅)₄ SiO₄).

In the embodiment in which the glass substrate 22 is a silica-soda limeglass, the coefficient of thermal expansion will be between 75 and95×10⁻⁷ per degree C. Under this embodiment the modified ceramic surfacewill be designed to have a coefficient of thermal expansion less thanthe substrate 22. The silica-metal oxide ceramics shown in TABLE 1-Awill produce surface modifications appropriate for the strengthening ofsoda lime glass articles.

TABLE 1-A Range of Coefficient Silica/Metal Oxide of Thermal CeramicsExpansion ×10⁻⁷ based on a metal oxide per degree C. Zinc Oxide (ZnO)52-59 Alumina (Al₂O₃) 48-80 Titania (TiO₂) 59-78 Zirconia (ZrO₂) 67-78

In practice metalorganic compounds of silicon and of one or more of themetals, Zn, Al, Ti, or Zr are combined in ratios to give a ceramiccoating with the appropriate coefficient of thermal expansion. Thismixture is then applied to the soda-lime glass article at a temperaturebetween the annealing and softening points (about 500° C. and 725° C.,respectively) of the glass.

In the embodiment in which the glass substrate 22 is a borosilicateglass, the coefficient of thermal expansion will be between 22 and68×10⁻⁷ per degree C. Under this embodiment the modified ceramic surfacewill be designed to have a coefficient of thermal expansion less thanthe substrate 22. The silica-metal oxide ceramics shown in TABLE 1-Bwill produce surface modifications appropriate for the strengthening ofborosilicate glass articles.

TABLE 1-B Range of Coefficient Silica/Metal Oxide of Thermal CeramicsExpansion ×10⁻⁷ based on a metal oxide per degree C. 95% Zinc Oxide(ZnO) +  8-27 5% Silica (SiO₂) Alumina (Al₂O₃) + Boric 14-28 Oxide(B₂O₃) 65% Zirconia (ZrO₂) + 23-28 35% Silica

In practice metalorganic compounds of silicon and of one or more of themetals, Zn, Al, Zr, or the non-metal B, are combined in ratios to give aceramic coating with the appropriate coefficient of thermal expansion.This mixture is then applied to the borosilicate glass article at atemperature between the annealing and softening points (about 500° C.and 800° C., respectively) of the glass.

As an alternate method of producing a chemically modified ceramicsurface multi-component formulations may also be used. Table 1-C setsforth specific examples of compositions with specified coefficients ofthermal expansion.

TABLE 1-C Coefficient Of Thermal Expansion × 10⁷ per degree C. 5 13 2432 33 Approximate Percentage of Member Member in Formulation SiO₂ 62 7070 62 64 Al₂O₃ 13 23 25 26 21 B₂O₃ 1.5 4 5 0 0 RO where R maybe 23.5 3 012 15 Ca, Mg or Sr Total Percentage 100 100 100 100 100

In manufacturing the composite article 20 of the present invention, theglass substrate 22 is maintained at a temperature above the annealingpoint (about 500° C.) and below the softening point (soda-lime about725° C.; borosilicate about 800° C.) of the glass and, while maintainedin this range, it is brought into contact with the appropriatemetalorganic mixture in an oxygen deficient atmosphere. This is done byspraying, atomizing, or otherwise providing a gaseous atmosphere foreffecting chemical vapor deposition by means known in the art.Sufficient time is allowed for the chemical reaction producing thechemically modified surface to occur.

The metalorganic compounds selected as carriers for Si (silicon) and foreach of the metals shown in TABLES 1-A and 1-B and 1-C are selected onthe basis of properties such as viscosity, reactivity, compatibility,and safety factors.

EXAMPLES

Using the teachings of this invention, two types of articles wereprepared to demonstrate the chemical modification of the surface and thesubsequent effect of enhancing the chemical durability and strength asmeasured by the modulus of rupture.

Example 1 Chemical Durability

In this example of the application of the teachings of this invention,small soda-lime glass containers similar to articles called baby foodjars were treated according to the requirements set forth above in thisinvention. For this example a 50:50 mixture of tetraethyl ortho-silicateand aluminum sec-butoxide was prepared by mixing equal volumes of thesemetalorganic compounds. This mixture was then applied as an atomizedspray to the hot bottle surfaces according to the teachings above. Thesamples were then allowed to cool such that they would then be annealedaccording to prior art. Other bottles of the same type were similarlytreated with the exception that they were not exposed to the mixture ofthe metalorganic chemicals specified above. These bottles were the“controls”. The Chemical Durability of the treated and untreated bottleswere then measured according to the procedure known as “Test Methods forResistance of Glass Containers to Chemical Attack”, ASTM C225-85, MethodB-W.

This procedure determines the volume of sulfuric acid (H₂SO₄) ofspecified concentration required to neutralize the alkali leached fromthe inside surface of the container under specific treatment conditions.The better the durability, the less alkali is leached from the containerwhich in turn is neutralized by a smaller volume of sulfuric acid thanthat required by a container of inferior durability. TABLE 2 shows theresults of the chemical durability test.

TABLE 2 ml of 0.020N H₂SO₄ Average ml of 0.020N H₂SO₄ UntreatedContainer Control 1 1.41 Control 2 1.34 Average 1.38 Treated Container#1 0.71 #3 0.83 #3 0.63 #4 0.59 Average 0.69* *In the ASTM method forchemical durability, a lower valve indicates improved durability.

It is seen from the data presented in TABLE 2 that the average chemicaldurability has been improved by a factor of 2, a 100% improvement, asthe result of the ceramic surface modification procedure taught by thisinvention.

Example 2 Strength (Modulus of Rupture)

In this example of the application of the teachings of this invention,soda lime glass rods ¼ inch diameter by approximately 7 inches long weretreated according to the requirements set forth above. For this examplea 50:50 mixture of tetraethyl ortho-silicate and aluminum sec-butoxidewas prepared by mixing equal volumes of these metalorganic compounds.This mixture was then applied as an atomized spray to the hot rodsurfaces according to the teachings above. The samples were then allowedto cool such that they would then be annealed according to prior art.Other rods of the same type were similarly treated with the exceptionthat they were not exposed to the mixture of the metalorganic chemicalsspecified above. These rods were the “controls”. The Modulus of Ruptureof the treated and untreated rods was then measured according to theprocedure known as “Method for Flexure Testing of Glass (Determinationof Modulus of Rupture)”, ASTM C158-80. This procedure determines theModulus of Rupture, a measure of the breaking strength. In this test anincreasing load measured in pounds is applied at a constant rate to theglass rod. The load L at break is then used in the following formula toevaluate the Modulus of Rupture in psi (pounds per square inch):

Modulus of Rupture=5.09₂*La/bd²

where a=1 inch (a value fixed by the dimensions of the device used toapply the breaking force in 2 point loading), b is the maximum diameterof the rod, and d is the minimum diameter. This corrects for theelipticity of the glass rod which is ordinarily not exactly round. TABLE3 shows the results of the Modulus of Rupture test.

TABLE 3 Modulus of Rupture, Average Modulus of Rupture psi psi UntreatedRods Control A-1 9,450 Control A-2 15,200 Control A-3 14,100 Control A-411,100 Control A-5 14,100 Average 12,800 Treated Rods B-1 28,800 B-221,600 B-3 15,600 B-4 26,800 B-5 18,900 B-6 19,400 B-7 19,800 B-8 22,700B-9 13,400 B-10 26,100 B-12 22,700 Average 21,400

It is seen from the data presented in TABLE 3 that the average Modulusof Rupture has been improved by a factor of 1.67, a 67% increase inaverage strength as the result of the ceramic surface modificationprocedure taught by this invention.

To further establish that the surface of the rods had been modified withrespect to their chemical composition, the surfaces of untreated controlrods and ceramic surface modified rods were examined for the presence ofaluminum using Electron Microprobe techniques. In this measurement therod is placed in an high vacuum and bombarded with high energy electronsfocused to a small spot on the surface of the rod. The electrons causethe atoms in the surface of the glass to emit their own characteristicx-rays with an intensity proportional to the concentration of atoms ator near the surface of the rod. Thus, by comparing the intensities ofthe characteristic Al Ka x-rays emitted by the aluminum atoms in thecontrol sample with those emitted by the aluminum atoms of the ceramicsurface modified rods, it was possible to confirm that the treatmenttaught by this invention modified the surface of the treated rods.

In this procedure both the untreated control rods and ceramic surfacemodified rods were cleaned in an ultrasonic bath to remove anymechanically adhering particles or dust of silica or alumina which hadnot chemically reacted with the substrate glass, 22 in FIG. 2. Theresults of the Electron Microprobe studies are shown in TABLE 4.

TABLE 4 Intensity of Intensity of Al Ka X-Rays, Treated Rods Al Ka cpsCleaned X-Rays, cps Untreated Rods Cleaned Control A-1  25 (ExteriorSurface) Control A-1  22 (Interior Fracture Surface) Average 24 TreatedRods (Exterior Surface) Cleaned B-1 239 B-3 113 B-4 132 B-9 134 Average155

It is seen from the data presented in TABLE 4 that the average Al Kax-ray intensity from the Aluminum atoms in the ultra-sonically cleanedsurface of rods having the ceramic surface modification preparedaccording to the teachings of this invention is significantly greaterthan the corresponding intensity from untreated control rods by a factorof 6.5 or 550%. The chemically applied ceramic surface modificationprepared according to the teachings of this invention has an aluminumconcentration significantly greater than in the untreated control.

The microprobe analysis amply demonstrates that the surface of the rods,24 of FIG. 2, has been substantially modified by applying the techniquesof this invention to the substrate 22 of FIG. 2.

Many modifications will become readily apparent to those skilled in theart. Accordingly, the scope of the present invention should bedetermined only by the scope of the appended claims.

We claim:
 1. A method of forming a glass composite article comprising the steps of: (a) providing a glass substrate having a predetermined coefficient of thermal expansion; (b) maintaining said substrate at a temperature above the annealing point and below the softening point temperatures; (c) bringing said substrate maintained within said temperature range into contact with an atmosphere of a mixture of metalorganic compounds and silicon organic compounds; (d) causing the mixture to decompose and react with the substrate to produce a metallic ceramic surface having a lower coefficient of thermal expansion than the glass substrate, and to produce a transition layer comprising a mixture of the metallic ceramic surface and the glass substrate; and (e) cooling the composite article wherein the lower coefficient of thermal expansion holds the metallic ceramic surface in compression on the glass substrate.
 2. The method of forming a glass composite according to claim 1 wherein said step of causing the mixture to decompose and react with the substrate to produce the ceramic surface is enhanced by the absorption of infrared energy at the surface of said article.
 3. The method of forming a glass composite according to claim 2, wherein said infrared energy has a peak energy at one micron wavelength.
 4. The method of forming a glass composite according to claim 1 wherein said substrate has a coefficient of thermal expansion on the range of 75 to 95×10⁻⁷ per degree C. and said chemically modified ceramic surface has a coefficient of thermal expansion between 48 and 80×10⁻⁷ per degree C.
 5. The method according to claim 1 wherein the mixture of metal organic compounds and silicon organic compounds is a mixture of a metal alkoxide and silicon alkoxide.
 6. The method according to claim 5 wherein the alkoxides are represented by the formulas R_(n)XO_(n) and R₄SiO₄ wherein X is Al, Ti, Ta, Zr, In or Sn, each R group is an alkyl radical having 1 to 8 carbon atoms and n is an integer ranging from 1 to
 4. 7. The method according to claim 6 wherein each R group is an alkyl radical having 1 to 3 carbon atoms, X is Al and n is the integer
 3. 8. The method according to claim 5 wherein the mixture of organic compounds is a mixture of aluminum ethoxide ((C₂H₅)₃ ALO₃) and tetraethyl silicate ((C₂H₅)₄ SiO₄). 